If your dd and her friends feel welcome at your home, do you think they will spend more time at your house? And if so, is having her friends at your house whilst you are having dinner, a price you are willing to pay?
I think, looking at the bigger picture, it is better to make small compromises if that makes your house a welcoming place for your dd and her friends to hang out.
My dses know I am happy to welcome their friends here. Ds3 has a couple of friends whose parents are much more likely to get cross if they stay out too late or get pissed (they are 18) - I would rather he felt they can come back here than that they were wandering round the neighbourhood. And if ds3 has drunk too much, I would rather he came home so I can keep an eye on him than that he was out there somewhere, pissed as a fart.
He is part of a close group of friends - they look after eachother, which I think is very important - and I aim to foster that by being welcoming to his friends.
That said, I would be very cross if I asked his friends to leave because he had homework, and they refused! But if you give a little over the dinner time thing, you have every justification to say 'Look, dd, I have listened to you about dinner time, and your friends can stay whilst we eat - but if you have homework to do, then they do have to leave - I think that is a fair compromise.'